Revisist the `@defaultResponse` decorator

This decorator is in openapi and now with the addition of status code ranges it feels a lot less useful.

The problem with this decorator is that it changes the meaning of the operation response from openapi point of view but not from the http library.

So you have this weird thing there one user of the http library would get a different behavior than openapi3

If this is a feature we still want, what if it is just when the status code is an int but has no range
```
@error model ServerError {
@statusCode @minValue(500) @maxValue(599) _: int32;
}

@error model Default {
@statusCode _: int32;
}
op test(): Pet | ServerError | Default;
```